When making iron cores, or transformers of rotors equipped in motors, those have conventionally been pursued to have preferable magnetic characteristics such as high permeability or small holding power, and less iron loss.
Therefore, for avoiding generation of Joule heat caused by eddy currents as a main cause of the iron loss and generation of magnetic force in a counteracting direction, aiming at interception of the eddy current flow, it is considered to reduce in thickness an electromagnetic steel plate having good magnetic characteristic, and laminate plural sheets of thinned steel plates for producing iron cores or transformers of rotors.
In the above mentioned production, if there would exist a metal material which has superior characteristics concerned with permeability, iron loss, workability, strength characteristic, or corrosion resistance, such a metal material were very useful, but actually there does not exist one metal plate which would be excellent in various kinds of characteristics.
For example, an amorphous property has a very superior magnetic characteristic such as high permeability or low iron loss, but this is poor in the workability and hard to be formed.
The electromagnetic steel plate does not have the magnetic characteristic as the amorphous property, but is more excellent in the workability than the amorphous property.
A low carbon steel plate is inferior in the magnetic characteristics to the electromagnetic steel plate, but superior in the workability, cheap, and advantageous to cost down.
An electromagnetic soft steel plate is inferior in iron loss to the electromagnetic steel plate, but superior in the workability.
As mentioned above, individual metal plates have respective characteristics, but also have poor characteristics.
As a metal material composed by joining and laminating heterogeneous metal plates, there is a clad steel.
The clad steel is produced, for example, by metal-joining stainless steels to the upper surface and the rear surface of an intermediate layer of an ultra low carbon steel, or metal-joining a permalloy to the lower layer and the upper layer of the intermediate layer of the stainless steel, and the clad steel has many characteristics.
As methods of making one body by joining the laminated metal plates other than the above mentioned clad steel, such measures have been practiced as an embossing process, bondage by an bonding agent, or temporarily holding by rivets, said embossing process forming dotted concaves and dotted convexes in the metal plates and fitting the concaves and convexes.
However, in case of producing the laminated iron core of the motor, if the metal plates have thin thickness, a punching process of the iron core pieces increases for providing the laminated core of a desired laminated thickness, so that productivity lowers.
Then, for heightening the punching productivity, it is assumed to carry out punching through the laminated thin metal plates, but, for example, since the amorphous plate is inferior in the workability, if punching through the laminated thin metal plates, cracks or breakages are caused.
On the other hand, the clad steel necessitates heating at high temperatures and fuse-bonding treatment for metal-joining heterogeneous metals, considerable energy and labor are taken for the production, and high cost is invited.
Further, in the embossing process, a caulking strength by the concave and convex parts of the metal plates to be joined is weak, and might probably come off during processing or transportation.
Bonding by an bonding agent might be exfoliated by expansion of an air remaining between the metal plates to be bonded, impurities adhered to the bonded faces, or weak bonding force, and cost is high.
The joining by the rivets has a problem that parts of the rivets exist as the convexes on an opposite side of the jointed face of the metal plate, and if the convexes contact another metal plate, this metal plate takes scratches.
In view of the above mentioned actual circumstances, it is accordingly an object of the invention to provide a metal plate of laminated heterogeneous materials, and an iron core of laminated heterogeneous materials where a plurality of metal plates of different material qualities are easily and stably joined, have characteristics over many applications, and may attain low production cost, and provide a making method thereof.